Recently, there has been increasing interest in energy storage technology. Electrochemical devices have been widely used as energy sources in portable phones, camcorders, notebook computers, PCs and electric cars, resulting in intensive research and development. In this regard, electrochemical devices are subjects of great interest. Particularly, development of rechargeable secondary batteries has been the focus of attention.
Conventionally, as an electrolyte for an electrochemical device such as a battery using an electrochemical reaction, an electric dual layer capacitor, etc., an electrolyte in a liquid phase, especially an ion conductive organic liquid electrolyte in which salt is dissolved in a non-aqueous organic solvent has been mainly used.
However, when such an electrolyte in a liquid phase is used, there is a high possibility that an electrode material is deteriorated, and an organic solvent is volatilized. In addition, there may occur a safety problem, such as combustion by an increase of ambient temperature or a battery's own temperature. Particularly, in the case of a lithium secondary battery, there is a problem in that during charge/discharge, gas is generated within the battery by decomposition of a carbonate organic solvent, and/or a side reaction of the organic solvent and an electrode, thereby expanding a battery thickness. Also, through high storage, such a reaction is accelerated, thereby more significantly increasing the amount of the generated gas.
The continuously generated gas increases internal pressure of the battery, and thus causes deformation of the center on a certain portion of the battery, such as expansion of a prismatic battery in a certain direction. In addition, the gas makes a minute difference in adhesion on an electrode surface within the battery, and thus an electrode reaction cannot be uniformly carried out over the whole electrode surface, thereby causing the thickness to be non-uniformly formed. Accordingly, performance and safety of the battery are inevitably reduced.
In general, it is known that in the order of a liquid electrolyte <a gel-type polymer electrolyte <a solid polymer electrolyte, the safety of a battery is improved, but the battery performance is reduced. Due to such a low battery performance, batteries employing a solid polymer electrolyte have not yet been commercialized.
Meanwhile, a conventionally known manufacturing method of a battery using a gel-type polymer electrolyte includes the following two methods.
In one method, a battery including a gel-type polymer electrolyte is manufactured by the steps of: injecting a composition where a polymerizable monomer and a polymerization initiator are mixed with a liquid electrolyte including a non-aqueous organic solvent containing salt dissolved therein, into the battery including an electrode assembly in which a cathode, an anode, and a separator are wound or laminated; and subjecting the composition to gelation under appropriate temperature and time conditions.
However, in this method, a process for maintaining temperature for the gelation is required, thereby causing a loss in time and economic efficiency. Also, in a certain constituent ratio of the polymerizable monomer or the polymerization initiator, the gelation may be carried out at room temperature without a heating process, but there is a possibility that the gelation is carried out before composition injection into the battery.
In another method, a battery is manufactured by the steps of: coating a composition where a polymerizable monomer and a polymerization initiator are mixed with a liquid electrolyte including a non-aqueous organic solvent containing salt dissolved therein, on a separator; subjecting the composition to gelation by using heat or UV rays; assembling the separator with a cathode and an anode to manufacture the battery; and injecting a conventional liquid electrolyte to the battery.
However, in this method, a process of irradiating heat or UV for gelation is required. Also, the separator coated with gel may absorb moisture, thereby reducing performance and safety of the battery.